Method for operating an internal combustion engine

Abstract

A method for operating an internal combustion engine, in which fuel is injected into a combustion chamber of the internal combustion engine with the aid of an injector, a variable which characterizes a slope of a straight line or of a curve which has at least some sections in the shape of a straight line, being ascertained, the straight line or straight line-shaped curve linking activation times of the injector to the appropriate difference values, and a difference value being formed by the difference between an instantaneous closing point in time and a reference closing point in time or between an instantaneous injection quantity and a reference injection quantity, and a measure for a coking of the injector being ascertained from the ascertained variable.

1 . A method for operating an internal combustion engine, in which fuel is injected into a combustion chamber of the internal combustion engine with the aid of an injector, the method comprising:
 ascertaining a variable, which characterizes a slope of a straight line or of a curve which has at least some sections in the shape of a straight line, the straight line or straight line-shaped curve linking activation times of the injector to associated difference values;   forming a difference value by a difference between an instantaneous closing point in time and a reference closing point in time or between an instantaneous injection quantity and a reference injection quantity; and   ascertaining a measure for a coking of the injector from the ascertained variable.   
     
     
         2 . The method according to  claim 1 , wherein the reference closing point in time or the reference injection quantity is ascertained on an uncoked reference injector and is stored in a memory. 
     
     
         3 . The method according to  claim 1 , wherein the steps are carried out at a constant fuel pressure. 
     
     
         4 . The method according to  claim 1 , wherein a variable which corresponds to a greater slope is evaluated as an indication of more intensive coking than a variable which corresponds to a lesser slope. 
     
     
         5 . The method according to  claim 1 , wherein an activation of the injector is changed as a function of the ascertained coking in such a way that an actual injection quantity of fuel is corrected with respect to a setpoint injection quantity of fuel. 
     
     
         6 . The method according to  claim 1 , wherein the closing point in time is ascertained in that striking of a valve element on a valve seat of the injector is ascertained by evaluating an electrical signal applied to an electric actuator of the injector. 
     
     
         7 . The method according to  claim 1 , wherein, when it is determined that coking exists, an input is made into a memory which is readable by a diagnostic device. 
     
     
         8 . A non-transitory computer-readable medium containing a program which when executed by a processor performs the following method for operating an internal combustion engine, in which fuel is injected into a combustion chamber of the internal combustion engine with the aid of an injector:
 ascertaining a variable, which characterizes a slope of a straight line or of a curve which has at least some sections in the shape of a straight line, the straight line or straight line-shaped curve linking activation times of the injector to associated difference values;   forming a difference value by a difference between an instantaneous closing point in time and a reference closing point in time or between an instantaneous injection quantity and a reference injection quantity; and   ascertaining a measure for a coking of the injector from the ascertained variable.   
     
     
         9 . A control/regulating unit for an internal combustion engine, in which fuel is injected into a combustion chamber of the internal combustion engine with the aid of an injector, the unit comprising:
 an arrangement for ascertaining a variable, which characterizes a slope of a straight line or of a curve which has at least some sections in the shape of a straight line, the straight line or straight line-shaped curve linking activation times of the injector to associated difference values;   an arrangement for forming a difference value by a difference between an instantaneous closing point in time and a reference closing point in time or between an instantaneous injection quantity and a reference injection quantity; and   an arrangement for ascertaining a measure for a coking of the injector from the ascertained variable.